The present invention relates to a system for controlling a direct-current electric motor of a fan which is associated, in a motor vehicle, both with a radiator of a hydraulic engine-cooling system and with a condenser of an air-conditioning system for the passenger compartment of a motor vehicle.
Control systems of this type, in which the speed of rotation of the electric motor used can adopt one or more different but constant values, are known. The control of the speed of rotation of the fan motor in these systems has many disadvantages. This is due to the fact that the working conditions of the internal combustion engine of the motor vehicle are greatly variable, as are the ambient temperature conditions. If the fan motor is driven on the basis of the requirements of the engine cooling system, there is therefore a great risk that the air-conditioning system will operate in conditions which are not at all ideal and, in particular, with refrigerant-fluid pressures which are far from ideal.
A known solution which prevents these problems consists in the use of a two-speed motor with a resistor or of a second fan which is driven by an electric motor or is rotated by the engine of the motor vehicle, and which is intended to generate an air-flow in dependence on the requirements of the air-conditioning system with the objective of limiting the total electrical power necessary, particularly in intermediate operating conditions. This solution leads to problems from the point of view of costs and of the structural complexity and control of the system.
The object of the present invention is to provide a control system which can comply effectively with the ventilation requirements of the engine cooling system and of the air-conditioning or climate-control system for the passenger compartment, without requiring the use of an additional fan or of a motor with a resistor for changing the speed.
This and other objects are achieved, according to the invention, by a control system the main characteristics of which are defined in appended claim 1.